1. Field of the Invention
The present invention relates to a radiographic imaging device and method which radiographs a subject, such as a breast, to acquire a radiographic image, and in particular, to a radiographic imaging device and method suitable for radiographing a breast including an implant.
2. Description of the Related Art
In recent years, in order to promote early detection of breast cancer, image diagnosis using a radiographic imaging device (called mammography) for radiographing a breast has attracted attention. A radiographic image (breast image) of the breast radiographed by the mammography is subjected to image processing in a dedicated operation terminal or the like, and is used for diagnosis by a physician. The physician examines the presence or absence of a lesion, such as tumor or calcification, by displaying the breast image on a display and reading the breast image.
In the mammography, in order to acquire a high-quality breast image, it is necessary to set an appropriate irradiation condition of radiation according to radiation transmittance of a breast as a subject. In particular, when a subject is a breast, transmittance of radiation is significantly different according to the thickness of the breast and the density of a mammary gland. For this reason, it is necessary to appropriately set the irradiation condition of a tube voltage and a tube current of a radiation source, an irradiation time, the type of a target generating radiation, the type of a filter capable of selectively absorbing a high energy component or a low energy component of radiation, and the like according to the state of the breast, thereby preventing the breast from being irradiated with excessive radiation.
As a method of setting the irradiation condition, a method (see JP2012-096084A) has been suggested, in which an automatic exposure control (AEC) sensor, which detects the dose of radiation transmitted through the breast, is provided in the mammography, the subject is irradiated with a small dose of radiation, the dose of transmitted radiation is detected by the AEC sensor, pre-irradiation is performed to set an irradiation condition necessary for radiographing, and then, main irradiation is performed to irradiate the subject with radiation under the set irradiation condition, thereby acquiring a radiographic image. A method (see JP2007-236804A) has also been suggested, in which an irradiation condition of main irradiation is set by analyzing a pre-radiographic image obtained through pre-irradiation.
On the other hand, for example, there is a case where breast reconstructive surgery after breast cancer surgery or breast enlargement surgery for beauty treatment is performed for a breast to be radiographed, and in this case, an implant, such as silicon or physiological saline, is embedded in the breast. In a breast embedded with an implant and a breast embedded with no implant, breast images acquired by radiographing are significantly different in image quality. In particular, the implant has a small dose of transmitted radiation, and appears as a high-luminance region in the breast image.
It is preferable that the irradiation condition at the time of radiographing of the breast is set to match the mammary gland as a region of interest to be diagnosed. Since the mammary gland has a comparatively small transmission amount of radiation, in many cases, the irradiation condition is set based on a region where the transmission amount of radiation is comparatively small. However, if an implant is embedded in the breast, the irradiation condition is set based on the region of the implant where the transmission amount of radiation is small, and as a result, the breast may be irradiated with excessive radiation.
For this reason, in the mammography, a method (see JP2009-507595A) has been suggested, in which a region where the transmission amount of radiation is extremely small is detected as an implant region, and irradiation condition is set excluding the detected implant region. According to the method of JP2009-507595A, an irradiation condition which is suitable when an implant is embedded in a breast are set, whereby, even if an implant is embedded in the breast, it is possible to prevent the breast from being irradiated with excessive radiation.